1. Macbook Air
Which of these can be upgraded to the max for using the software(s)?
Best is a Mac Pro with 7200rpm SATA drives internally and a min of 8 (if not 12) GB RAM, and the best graphics card you can afford.
Second is an iMac maxed out on RAM, and the fastest CPU and best Graphics config you can afford.
Third would be a MacBook Pro, 17".
Graphics card is going to be the biggest factor here, second to CPU speed and how much RAM. But hard drives need to be 7200rpm, and don't put media on the OS drive for better performance. Internal is best, but FW800 is ok.